Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $70.85   8.622%   $76.9587   $76.96   $76.95   $77.00  
  Purchase #2 $187.60   10.348%   $207.0128   $207.01   $207.00   $207.00  
  Purchase #3 $84.65   12.494%   $95.2262   $95.23   $95.25   $95.20  
  Purchase #4 $98.42   3.393%   $101.7594   $101.76   $101.75   $101.80  
  Purchase #5 $243.82   8.259%   $263.9571   $263.96   $263.95   $264.00  
  Purchase #6 $237.93   11.429%   $265.123   $265.12   $265.10   $265.10  
  Purchase #7 $209.67   12.673%   $236.2415   $236.24   $236.25   $236.20  
  7 purchase totals = $1,132.94       $1,246.2787   $1,246.28   $1,246.25   $1,246.30